The course has a dual objective: a) to analyze the fundamentals of dyeing, interpreted as a two-phase process where dye mass transfer is regulated by kinetics as well by equilibrium between liquor and fibres, b) to provide a vision of the environmental impact of wet textile productions by analysing water need and pollutant load. In this context, updated solutions directed to water economization and to conceive an advanced wastewater treatment scheme aimed at recycling are discussed.

The first part of the course provides examples on dye to fibre chemical relationships to provide a frame of most common processes. Dyeing is described as a sequence of steps, considering liquor preparation, convection within the equipment, diffusion in the liquor-to-fibre boundary layer, adsorption at the interface, diffusion in the solid matrix and fixation of the dye to the fibre active sites. The adsorption equilibrium, representing the ultimate and optimal repartition of a dye between the two phases, is described according to adsorption models and related to the process working line. The process thermodynamics is considered to provide a fundamental interpretation of physical and chemical conditions put into practice during industrial operations. Dyeing kinetics is described according to most common models. Diffusional mass transfer follows Fick’s laws, either applied with constant diffusivity or considering this parameter affected by the process evolution. The parameters which affect dye diffusivity are considered to provide an estimate of apparent diffusivity related to the value of this property measured in the liquid according to a description in a porous system.
Dyeing equipment are given a general approach to describe the dynamic behaviour of mass transfer as a function of liquor flow rate, liquor- to-textile substrate mass ratio and dye affinity. Additionally, the evolution of dye distribution against to textile substrate thickness is considered to estimate coloration evenness.
A comprehensive description of the most important type of dyeing equipment is given for staple, yarn and fabric for batch processes. The structure of equipment with their major components (pressurized vessel, pumps, heat exchangers, ancillary vessels, etc.) is discussed in view of operations characterizing a dyeing diagram, including purging as well as various wash-off strategies.
Continuous dyeing, ageing at suitable temperatures according to fibre characteristics and final drying are presented.
The evaluation of coloration fastness is discussed according to the standards.

A synthetic panorama is given to list the major pollution sources in the textile sector, then alternative solutions, now at the development stage, are mentioned. Water needs and major categories of waste chemicals are given to define typical pollution parameters. A panorama of acting laws in different countries as reference frames to which technologies should aim at. The wastewater state of the art is presented as a starting point from which develop novel treatment schemes and then a panorama of BATs is illustrated to define how to reach the necessary water quality specifications to accomplish recycling. A brief presentation of an extensive research program carried out by an Industry/Academia is illustrated as an effective tool to generate suitable know-how.
The second part of the course will work on actual industrial data to design an installed base model and integrate the management of a dye-house together with an advanced wastewater treatment plant. The following steps will be considered:
- choice of dyeing equipment to rationalize water consumption,
- choice of basic dyeing diagrams and their development according to an engineering representation;
- evaluation of typical pollution parameters;
- design of a sewer infrastructure;
- design of primary wastewater treatment stages;
- comparative design of aerated secondary wastewater treatment stages;
- selection of tertiary wastewater treatment stages: design of GAC units, ozone treatment units, standard and tangential filtration systems;
- use of case study PFD and P&IdD diagrams

Guided classroom exercitations will be carried out and a one-day visit to a dyeing factory and to an experimental wastewater treatment platform are planned